1. Field of the Invention
The present invention relates to an integrated semiconductor optical device used for optical communication, optical recording, optical measurement, or the like.
2. Description of the Related Art
In recent years, an integrated semiconductor optical device in which a gain region (light emitting region) or a semiconductor laser device and another semiconductor optical device such as an optical modulator, an optical amplifier, or an optical multiplexer and demultiplexer are integrated on a single semiconductor substrate has been developed. To couple a semiconductor laser device with another semiconductor optical device optically, for example, a butt joint method is employed. Japanese Unexamined Patent Application Publication No. 2008-66318 (Patent Document 1) describes a semiconductor wavelength tunable laser in which a gain region and a ring resonator have been joined together by a butt joint method. In this semiconductor wavelength tunable laser, the gain region and the ring resonator have mesa-type optical waveguide structures that are composed of different materials and have different mesa structures, respectively.